382 research outputs found
Perturbative operator approach to high-precision light-pulse atom interferometry
Light-pulse atom interferometers are powerful quantum sensors, however, their
accuracy for example in tests of the weak equivalence principle is limited by
various spurious influences like magnetic stray fields or blackbody radiation.
Pushing the accuracy therefore requires a detailed assessment of the size of
such deleterious effects. Here, we present a systematic operator expansion to
obtain phase shifts and contrast analytically in powers of the perturbation.
The result can either be employed for robust straightforward order-of-magnitude
estimates or for rigorous calculations. Together with general conditions for
the validity of the approach, we provide a particularly useful formula for the
phase including wave-packet effects
Modeling many-particle mechanical effects of an interacting Rydberg gas
In a recent work [Phys. Rev. Lett. 98, 023004 (2007)] we have investigated
the influence of attractive van der Waals interaction on the pair distribution
and Penning ionization dynamics of ultracold Rydberg gases. Here we extend this
description to atoms initially prepared in Rydberg states exhibiting repulsive
interaction. We present calculations based on a Monte Carlo algorithm to
simulate the dynamics of many atoms under the influence of both repulsive and
attractive longrange interatomic forces. Redistribution to nearby states
induced by black body radiation is taken into account, changing the effective
interaction potentials. The model agrees with experimental observations, where
the ionization rate is found to increase when the excitation laser is
blue-detuned from the atomic resonance
Selective Photocyclization of Amino Acids in Dipeptides
Amino acids in dipeptides which are substituted at the N-atom by a benzoylalkyl group can be selectively photocyclized via a triplet biradical. With valine as amino acid the cyclization leads mainly to one product out of eight possible isomers
Universality-of-Clock-Rates Test using Atom Interferometry with Scaling
We propose a competitive quantum test of the universality of clock rates that
depends on the proper time of a freely-falling particle, scaling cubic with the
laboratory time. In contrast to current tests with fountain clocks, our
proposed atom-interferometric scheme can be made robust against initial
conditions and recoil effects, making optical frequencies accessible even for
long interferometer durations. We study the influence of parasitic effects and
discuss implementations with strontium isotopes that may even outperform
current tests with fountain clocks.Comment: 9 pages, 3 figures, 1 tabl
Influence of cell shape, inhomogeneities and diffusion barriers in cell polarization models
In silico experiments bear the potential to further the understanding of biological transport processes by allowing a systematic modification of any spatial property and providing immediate simulation results for the chosen models. We consider cell polarization and spatial reorganization of membrane proteins which are fundamental for cell division, chemotaxis and morphogenesis. Our computational study is motivated by mating and budding processes of S. cerevisiae. In these processes a key player during the initial phase of polarization is the GTPase Cdc42 which occurs in an active membrane-bound form and an inactive cytosolic form. We use partial differential equations to describe the membrane-cytosol shuttling of Cdc42 during budding as well as mating of yeast. The membrane is modeled as a thin layer that only allows lateral diffusion and the cytosol is modeled as a volume. We investigate how cell shape and diffusion barriers like septin structures or bud scars influence Cdc42 cluster formation and subsequent polarization of the yeast cell. Since the details of the binding kinetics of cytosolic proteins to the membrane are still controversial, we employ two conceptual models which assume different binding kinetics. An extensive set of in silico experiments with different modeling hypotheses illustrate the qualitative dependence of cell polarization on local membrane curvature, cell size and inhomogeneities on the membrane and in the cytosol. We examine that spatial inhomogenities essentially determine the location of Cdc42 cluster formation and spatial properties are crucial for the realistic description of the polarization process in cells. In particular, our computer simulations suggest that diffusion barriers are essential for the yeast cell to grow a protrusion
Interference of Clocks: A Quantum Twin Paradox
The phase of matter waves depends on proper time and is therefore susceptible
to special-relativistic (kinematic) and gravitational time dilation (redshift).
Hence, it is conceivable that atom interferometers measure general-relativistic
time-dilation effects. In contrast to this intuition, we show that light-pulse
interferometers without internal transitions are not sensitive to gravitational
time dilation, whereas they can constitute a quantum version of the
special-relativistic twin paradox. We propose an interferometer geometry
isolating the effect that can be used for quantum-clock interferometry.Comment: 9 Pages, 2 Figure
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